Gate-all-around integrated circuit structures having depopulated channel structures using multiple bottom-up oxidation approaches

ABSTRACT

Gate-all-around integrated circuit structures having depopulated channel structures, and methods of fabricating gate-all-around integrated circuit structures having depopulated channel structures using multiple bottom-up oxidation approaches, are described. For example, an integrated circuit structure includes a vertical arrangement of nanowires. All nanowires of the vertical arrangement of nanowires are oxide nanowires. A gate stack is over the vertical arrangement of nanowires, around each of the oxide nanowires. The gate stack includes a conductive gate electrode.

TECHNICAL FIELD

Embodiments of the disclosure are in the field of integrated circuit structures and processing and, in particular, gate-all-around integrated circuit structures having depopulated channel structures, and methods of fabricating gate-all-around integrated circuit structures having depopulated channel structures.

BACKGROUND

For the past several decades, the scaling of features in integrated circuits has been a driving force behind an ever-growing semiconductor industry. Scaling to smaller and smaller features enables increased densities of functional units on the limited real estate of semiconductor chips. For example, shrinking transistor size allows for the incorporation of an increased number of memory or logic devices on a chip, lending to the fabrication of products with increased capacity. The drive for ever-more capacity, however, is not without issue. The necessity to optimize the performance of each device becomes increasingly significant.

In the manufacture of integrated circuit devices, multi-gate transistors, such as tri-gate transistors, have become more prevalent as device dimensions continue to scale down. In conventional processes, tri-gate transistors are generally fabricated on either bulk silicon substrates or silicon-on-insulator substrates. In some instances, bulk silicon substrates are preferred due to their lower cost and because they enable a less complicated tri-gate fabrication process. In another aspect, maintaining mobility improvement and short channel control as microelectronic device dimensions scale below the 10 nanometer (nm) node provides a challenge in device fabrication. Nanowires used to fabricate devices provide improved short channel control.

Scaling multi-gate and nanowire transistors has not been without consequence, however. As the dimensions of these fundamental building blocks of microelectronic circuitry are reduced and as the sheer number of fundamental building blocks fabricated in a given region is increased, the constraints on the lithographic processes used to pattern these building blocks have become overwhelming. In particular, there may be a trade-off between the smallest dimension of a feature patterned in a semiconductor stack (the critical dimension) and the spacing between such features.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A illustrates cross-sectional views representing a gate-all-around integrated circuit structure having a depopulated channel structure.

FIG. 1B illustrates cross-sectional views representing another gate-all-around integrated circuit structure having a depopulated channel structure.

FIG. 2 illustrates cross-sectional views representing various operations in a method of fabricating a gate-all-around integrated circuit structure having a depopulated channel structure, in accordance with an embodiment of the present disclosure.

FIGS. 3A-3D illustrate cross-sectional views representing various operations in a method of fabricating another gate-all-around integrated circuit structure having a depopulated channel structure, in accordance with an embodiment of the present disclosure.

FIGS. 4A-4J illustrates cross-sectional views of various operations in a method of fabricating a gate-all-around integrated circuit structure, in accordance with an embodiment of the present disclosure.

FIG. 5 illustrates a cross-sectional view of a non-planar integrated circuit structure as taken along a gate line, in accordance with an embodiment of the present disclosure.

FIG. 6 illustrates cross-sectional views taken through nanowires and fins for a non-endcap architecture (left-hand side (a)) versus a self-aligned gate endcap (SAGE) architecture (right-hand side (b)), in accordance with an embodiment of the present disclosure.

FIG. 7 illustrate cross-sectional views representing various operations in a method of fabricating a self-aligned gate endcap (SAGE) structure with gate-all-around devices, in accordance with an embodiment of the present disclosure.

FIG. 8A illustrates a three-dimensional cross-sectional view of a nanowire-based integrated circuit structure, in accordance with an embodiment of the present disclosure.

FIG. 8B illustrates a cross-sectional source or drain view of the nanowire-based integrated circuit structure of FIG. 8A, as taken along the a-a′ axis, in accordance with an embodiment of the present disclosure.

FIG. 8C illustrates a cross-sectional channel view of the nanowire-based integrated circuit structure of FIG. 8A, as taken along the b-b′ axis, in accordance with an embodiment of the present disclosure.

FIGS. 9A-9E illustrate three-dimensional cross-sectional views representing various operations in a method of fabricating a nanowire portion of a fin/nanowire structure, in accordance with an embodiment of the present disclosure.

FIG. 10 illustrates a computing device in accordance with one implementation of an embodiment of the disclosure.

FIG. 11 illustrates an interposer that includes one or more embodiments of the disclosure.

DESCRIPTION OF THE EMBODIMENTS

Gate-all-around integrated circuit structures having depopulated channel structures, and methods of fabricating gate-all-around integrated circuit structures having depopulated channel structures, are described. In the following description, numerous specific details are set forth, such as specific integration and material regimes, in order to provide a thorough understanding of embodiments of the present disclosure. It will be apparent to one skilled in the art that embodiments of the present disclosure may be practiced without these specific details. In other instances, well-known features, such as integrated circuit design layouts, are not described in detail in order to not unnecessarily obscure embodiments of the present disclosure. Furthermore, it is to be appreciated that the various embodiments shown in the Figures are illustrative representations and are not necessarily drawn to scale.

Certain terminology may also be used in the following description for the purpose of reference only, and thus are not intended to be limiting. For example, terms such as “upper”, “lower”, “above”, and “below” refer to directions in the drawings to which reference is made. Terms such as “front”, “back”, “rear”, and “side” describe the orientation and/or location of portions of the component within a consistent but arbitrary frame of reference which is made clear by reference to the text and the associated drawings describing the component under discussion. Such terminology may include the words specifically mentioned above, derivatives thereof, and words of similar import.

Embodiments described herein may be directed to front-end-of-line (FEOL) semiconductor processing and structures. FEOL is the first portion of integrated circuit (IC) fabrication where the individual devices (e.g., transistors, capacitors, resistors, etc.) are patterned in the semiconductor substrate or layer. FEOL generally covers everything up to (but not including) the deposition of metal interconnect layers. Following the last FEOL operation, the result is typically a wafer with isolated transistors (e.g., without any wires).

Embodiments described herein may be directed to back end of line (BEOL) semiconductor processing and structures. BEOL is the second portion of IC fabrication where the individual devices (e.g., transistors, capacitors, resistors, etc.) are interconnected with wiring on the wafer, e.g., the metallization layer or layers. BEOL includes contacts, insulating layers (dielectrics), metal levels, and bonding sites for chip-to-package connections. In the BEOL part of the fabrication stage contacts (pads), interconnect wires, vias and dielectric structures are formed. For modern IC processes, more than 10 metal layers may be added in the BEOL.

Embodiments described below may be applicable to FEOL processing and structures, BEOL processing and structures, or both FEOL and BEOL processing and structures. In particular, although an exemplary processing scheme may be illustrated using a FEOL processing scenario, such approaches may also be applicable to BEOL processing. Likewise, although an exemplary processing scheme may be illustrated using a BEOL processing scenario, such approaches may also be applicable to FEOL processing.

One or more embodiments described herein are directed to self-aligned bottom-up oxidation for nanowire transistor channel depopulation and nanoribbon transistor channel depopulation.

To provide context, integration of nanowire and/or nanoribbon complementary metal oxide semiconductor (CMOS) transistors is faced with the challenge of creating devices with different strengths. In the current FinFET technology, device strength granularity is achieved by varying the number of fins in the device channel. This option is unfortunately not easily available for nanowire and nanoribbon architectures since the channels are vertically stacked. This requirement is even more punishing for nanowire and/or nanoribbon (NW/NR) structures in a self-aligned stacked CMOS structure where NMOS and PMOS channels are patterned at the same width. Previous attempts to address the above issues have included (1) integrating NW/NR devices with different channel widths (an option only available for nanoribbon that requires complex patterning), or (2) subtractively removing wires/ribbon from source/drain or channel regions (an option challenging for stacked CMOS architectures).

To provide further context, transistors with different drive currents may be needed for different circuit types. Embodiments disclosed herein are directed to achieving different drive currents by de-populating (de-pop) the number of nanowire transistor channels in device structures. One or more embodiments provide an approach for deleting discrete numbers of wires from a transistor structure. Approaches may be suitable for both ribbons and wires (RAW). Furthermore, transistor leakage current flowing through a sub-fin must be controlled for proper circuit function. Embodiments disclosed herein provide a method for sub-fin isolation for nanowire transistors. For de-pop, technologies using FinFETs can de-populate the number of fins in each device to achieve different drive-current strengths. For sub-fin isolation, sub-fin implants are used to dope a sub-fin to reduce leakage. However, since nanowires are stacked and self-aligned, they cannot be de-populated (de-popped) the same ways as fins. Additionally, sub-fin dopants must be targeted and can back-diffuse into the channel, degrading carrier transport.

In accordance with an embodiment of the present disclosure, described herein is a process flow for achieving self-aligned bottom-up oxidation nanowire transistor channel de-population and/or sub-fin isolation. Embodiments may include channel de-population of nanowire transistors to provide for modulation of drive currents in different devices, which may be needed for different circuits. Embodiments may be implemented as a self-aligned approach allowing deep-scaling for future nanowire technologies.

In accordance with an embodiment of the present disclosure, nanowire processing of an alternating Si/SiGe stack includes patterning the stack into fins. Generic dummy gates (which may or may not be poly dummy gates) are patterned and etched. During a replacement gate process, NW/NR channels are released in an opened gate trench. Following NW/NR channel release, a thin film oxidation catalysts layer (e.g., Al₂O₃) is deposited on the NW/NR channels, e.g., using an atomic layer deposition (ALD) process. In a particular embodiment, a masking film (such as a carbon hardmask (CHM)) is then deposited to fill the gate trench, followed by a recess etch to leave CHM covering the ribbons to be converted into oxide. The oxidation catalysts layer is then removed from the exposed ribbons using a selective wet etchant such as dilute hydrogen fluoride or aqueous ammonium hydroxide-peroxide solution. The hardmask is then subsequently removed by exposing it to oxygen plasma to leave the oxidation catalyst layer (e.g., Al₂O₃) encapsulating only the bottommost one or more NW/NR channels. The bottommost one or more NW/NR channels are then selectively converted into an oxide (e.g., a silicon oxide from oxidizing silicon NW/NR channels) by subjecting them to a wet oxidation anneal. Since the oxidation catalyst layer (e.g., Al₂O₃) promotes oxygen diffusion into silicon (Si), the bottommost one or more NW/NR channels are rapidly converted to oxide (e.g., SiO₂). The oxidation condition selected may be very mild such that little oxidation occurs on the upper ribbons that are not encapsulated by the oxidation catalysts layer. In this way, Si nanowires are oxidized from the bottom-up. Although some embodiments describe the use of Si (wire or ribbon) and SiGe (sacrificial) layers, other pairs of semiconductor materials which can be alloyed and grown epitaxially could be implemented to achieve various embodiments herein, for example, InAs and InGaAs, or SiGe and Ge. Embodiments described herein enable the fabrication of self-aligned stacked transistors with variable numbers of active nanowires or nanoribbons in the channel, and methods to achieve such structures.

As a comparison of channel depopulation involving source or drain structure tuning, FIG. 1A illustrates cross-sectional views (gate cut on fin, and fin cut on gate) representing a gate-all-around integrated circuit structure having a depopulated channel structure.

Referring to FIG. 1A, a CMOS integrated circuit structure 100 is formed above a substrate 102 and includes a lower PMOS region and an upper NMOS region. The lower PMOS region includes stacked nanoribbons 104A, 104B, 104C and 104D. P-type source or drain structures 106 are adjacent the stacked nanoribbons and above an insulating structure 108. A lower gate structure includes a gate dielectric layer 110 having a P-type gate electrode 112 thereon. The upper NMOS region includes stacked nanoribbons 114A, 114B, 114C and 114D. N-type source or drain structures 116 are adjacent the stacked nanoribbons and above an insulating structure 118. An upper gate structure includes a gate dielectric layer 120 having an N-type gate electrode 122 thereon. Spacers 124 may be adjacent to an uppermost portion of the upper gate structure.

Referring again to FIG. 1A, all of the upper stacked nanoribbons 114A, 114B, 114C and 114D (e.g., in this case 4) are coupled to the N-type source or drain structures 116. However, only the upper two stacked nanoribbons 104C and 104D are coupled to the P-type source or drain structures 106, while the lower two stacked nanoribbons 104A and 104B are not coupled to the P-type source or drain structures 106. The resulting structure effectively depopulates two of the four channel regions of the P-type portion of the CMOS integrated circuit structure 100. However, source or drain 106 depth engineering is required to fabricate CMOS integrated circuit structure 100. It is to be appreciated that although the illustrative example of four upper wires and two lower wires and effectively two depopulated nanowires is depicted and described above, it is to be appreciated that all such wire counts may be varied.

As a comparison of channel depopulation involving channel count tuning, FIG. 1B illustrates cross-sectional views (gate cut on fin, and fin cut on gate) representing another gate-all-around integrated circuit structure having a depopulated channel structure.

Referring to FIG. 1B, a CMOS integrated circuit structure 150 is formed above a substrate 152 and includes a lower PMOS region and an upper NMOS region. The lower PMOS region includes stacked nanoribbons 154A and 154B above a raised substrate portion 158. P-type source or drain structures 156 are adjacent the stacked nanoribbons. A lower gate structure includes a gate dielectric layer 160 having a P-type gate electrode 162 thereon. The upper NMOS region includes stacked nanoribbons 164A, 164B, 164C and 164D. N-type source or drain structures 166 are adjacent the stacked nanoribbons and above an insulating structure 168. An upper gate structure includes a gate dielectric layer 170 having an N-type gate electrode 172 thereon. Spacers 174 may be adjacent to an uppermost portion of the upper gate structure.

Referring again to FIG. 1B, all of the upper stacked nanoribbons 164A, 164B, 164C and 164D (e.g., in this case 4) are coupled to the N-type source or drain structures 166. Also, both of the nanoribbons 154A and 154B are coupled to the P-type source or drain structures 156. However, the lower structure only includes two stacked nanoribbons 104A and 104B. The resulting structure effectively depopulates two of four channel regions of the P-type portion of the CMOS integrated circuit structure 150. However, channel count engineering is required to fabricate CMOS integrated circuit structure 150. It is to be appreciated that although the illustrative example of four upper wires and two lower wires and effectively two depopulated nanowires is depicted and described above, it is to be appreciated that all such wire counts may be varied.

As an example of a single bottom-up oxidation approach for channel depopulation, FIG. 1B illustrates cross-sectional views representing various operations in a method of fabricating a gate-all-around integrated circuit structure having a depopulated channel structure, in accordance with an embodiment of the present disclosure.

Referring to part (a) of FIG. 2 , a method of fabricating an integrated circuit structure includes forming a vertical arrangement 200 of active nanowires or nanoribbons above a substrate. For example, a lower set of nanowires 204A, 204B, 204C and 204D and an upper set of nanowires 214A, 214B, 214C and 214D are provided as a vertical stack. As explained in greater detail in other embodiments described below, channel regions of the lower set of nanowires 204A, 204B, 204C and 204D and the upper set of nanowires 214A, 214B, 214C and 214D may be exposed during a replacement gate process during which an open trench 203, such as an open trench formed in a dielectric layer or within dielectric spacers (either scenario represented as 202).

Referring to part (b) of FIG. 2 , an oxidation catalyst layer 230 is formed on the lower set of nanowires 204A, 204B, 204C and 204D, and the upper set of nanowires 214A, 214B, 214C and 214D. In one embodiment, the oxidation catalyst layer 230 is further formed along surfaces of the trench 202, as is depicted. In one embodiment, the oxidation catalyst layer 230 is or includes aluminum oxide. In another embodiment, the oxidation catalyst layer 230 is or includes lanthanum oxide.

Referring to part (c) of FIG. 2 , the oxidation catalyst layer 230 is patterned to confine the oxidation catalyst layer 230 only to those nanowires selected for channel depopulation. In an embodiment, a hardmask layer 232, such as a carbon-based hardmask layer, is formed in trench 203 on oxidation catalyst layer 230. The hardmask later 232 is then recessed to a level slightly above the uppermost nanowire selected for oxidation. The portions of oxidation catalyst layer 230 not covered by the recessed hardmask layer 232 are then removed to form oxidation catalyst portions 234.

Referring to part (d) of FIG. 2 , the hardmask layer 232 is removed. An oxidation process is then performed. In an embodiment, the oxidation process is a process that can oxidize silicon but at a rate that is substantially enhanced by the presence of oxidation catalyst portions 234. In one such embodiment, the oxidation process is enhanced to rapidly oxidize nanowires 204A and 204B to form oxide nanowires 250A and 250B, respectively, without oxidizing (or only very minimally oxidizing) nanowires 204C, 204D, 214A, 214B, 24C and 214D. In an embodiment, the oxidation process involves a wet oxidation anneal, e.g., heating the structure in the presence of water or water vapor. The approach effectively enables oxidizing one or more bottommost nanowires of the vertical arrangement of active nanowires but not one or more uppermost nanowires of the vertical arrangement of active nanowires.

It is to be appreciated that while six upper nanowires are selected to remain active and two lower nanowires are selected for oxidation on FIG. 2 , any suitable number of upper active nanowires may be retained while one or more lower nanowires are oxidized to form oxide nanowires.

It is also to be appreciated that following the processing described in association with part (d) of FIG. 2 , a permanent gate structure may be fabricated in trench 203. In one exemplary embodiment, the permanent gate structure includes a lower gate dielectric and lower P-type gate electrode thereon, and an upper gate dielectric and upper N-type gate electrode thereon. In another exemplary embodiment, the permanent gate structure includes a lower gate dielectric and lower N-type gate electrode thereon, and an upper gate dielectric and upper P-type gate electrode thereon. In an embodiment, the permanent gate structure is formed around all NW/NR channels, including the oxide NW/NR channels. In a particular such embodiment, the oxidation catalyst layer is not removed, and the remainder is included in the final structure. In other embodiments, however, the oxidation catalyst layer is removed prior to permanent gate structure fabrication.

With reference again to part (d) of FIG. 2 and the subsequent description, in accordance with an embodiment of the present disclosure, an integrated circuit structure includes a vertical arrangement of nanowires (e.g., 250A, 250B, 204C, 204D, 214A, 214B, 214C and 214D) above a substrate. The vertical arrangement of nanowires has one or more active nanowires (e.g., 204C, 204D, 214A, 214B, 214C and 214D) above one or more oxide nanowires (e.g., 250A and 250B). A gate stack is over the vertical arrangement of nanowires and around the one or more oxide nanowires (e.g., 250A and 250B).

In an embodiment, the one or more oxide nanowires (e.g., 250A and 250B) have an oxidation catalyst layer 234 thereon, e.g., as a residual layer or artifact layer remaining from a bottom-up channel depopulation process. In one embodiment, the oxidation catalyst layer 234 includes aluminum oxide. In another embodiment, the oxidation catalyst layer 234 includes lanthanum oxide.

In an embodiment, the integrated circuit structure includes epitaxial source or drain structures at ends of the vertical arrangement of nanowires. In one such embodiment, the epitaxial source or drain structures are discrete epitaxial source or drain structures, structural examples of which are described below. In another such embodiment, the epitaxial source or drain structures are non-discrete epitaxial source or drain structures, structural examples of which are described below. In an embodiment, the gate stack has dielectric sidewall spacers, and the epitaxial source or drain structures are embedded epitaxial source or drain structures extending beneath the dielectric sidewall spacers of the gate stack, structural examples of which are described below.

In an embodiment, the integrated circuit structure further includes a pair of conductive contact structures coupled to the epitaxial source or drain structures. In one such embodiment, the pair of conductive contact structures is an asymmetric pair of conductive contact structures, structural examples of which are described below.

In an embodiment, the vertical arrangement of nanowires is over a fin, structural examples of which are described below. In an embodiment, the gate stack includes a high-k gate dielectric layer and a metal gate electrode.

It is to be appreciated that embodiments described herein may be implemented to fabricate nanowire and/or nanoribbon structures having a different number of active wire/ribbon channel. It is to be appreciated that embodiments described herein may involve selective oxidation approaches to achieve such structures. Embodiments described herein may be implemented to enable the fabrication of nanowire/nanoribbon-based CMOS architectures.

In an embodiment, in order to engineer different devices having different drive-current strengths, a self-aligned depopulation (de-pop) flow can be patterned with lithography so that ribbons and wires (RAW) are de-popped only from specific devices. In an embodiment, the entire wafer may be de-popped uniformly so all devices have same number of RAW. It is to be appreciated that when de-pop is performed through a gate trench, some an epitaxial (epi) source or drain (S/D) materials may be oxidized from proximate the gate electrode, which is distinct from performing de-pop through a S/D location.

In another aspect, front-to-back vias may be fabricated through depopulated gate regions. Embodiments described herein may provide for a space-efficient way to transmit signals from front-side interconnects to backside interconnects (or vice versa) that does not necessarily involve extreme etches or extra patterning operations.

To provide context, the fabrication of state-of-the-art vias that transmit either signal or power from one side of a wafer to the other side of the wafer requires additional lithographic patterning and aggressive etches that can damage surrounding materials. Such prior approaches have designs that allow the via to short to neighboring source or drain regions. However, such shorting may not be allowed in the current design of the self-aligned transistors.

In accordance with one or more embodiments of the present disclosure, a fin, nanowire, or nanoribbon structure, or the like, is fabricated to include a conductive via structure in a self-aligned transistor technology. In a particular embodiment, a front-to-back via occupies the space of a gate region that has had all of its corresponding channels depopulated. In one embodiment, the via is composed of the same gate metal(s) as the surrounding active gate regions. The via connects to the front-side and backside interconnects in the same was as surrounding active gate regions.

Advantages to implementing embodiments described herein include enabling the ability to fabricate a front-to-back via that does not necessarily require additional lithographic patterning operations, e.g., since depopulation processing is already required elsewhere in a self-aligned transistor processing flow. Embodiments may also be implemented to allow for a front-to-back via that does not necessarily need extremely aggressive etches that otherwise damage surrounding materials (e.g., gate spacers, isolation caps/walls, plugs, etc.).

As an overview, in an embodiment, a self-aligned transistor is fabricated through polysilicon (or other dummy) gate removal. The transistor channels are revealed in the gate regions. Upon exposure of the transistor channels, portions of the channels can be depopulated, as defined by lithographic patterning. In an example, depopulation can be achieved through catalytic oxidation, e.g., in which a thin metal oxide (e.g., Al₂O₃ or La₂O₃) is conformally deposited around certain channels to increase the oxidation rate relative to channels without the metal oxide thereon.

As an exemplary double oxidation processing scheme, FIGS. 3A-3D illustrate cross-sectional views representing various operations in a method of fabricating another gate-all-around integrated circuit structure having a depopulated channel structure, in accordance with an embodiment of the present disclosure. It is to be appreciated that although demonstrated as two groups of three nanowires in each transistor region, any number of groupings, number of channels in each grouping, or channel geometry (e.g., nanoribbon, nanowire, fin) may be used.

Referring to FIG. 3A, a method of fabricating an integrated circuit structure includes forming a vertical arrangement 300 of active nanowires or nanoribbons above a substrate 302. Several adjacent device locations, such as device locations 330A, 330B and 330C, may be fabricated adjacent one another. In an embodiment, gate endcap structures separate the device locations 330A, 330B and 330C. In one such embodiment, each of the gate endcap structures are seated in a trench isolation layer 320A and include a liner dielectric layer 320B and a fill dielectric layer 320C. A dielectric cap 320D may be formed on each of the endcap structures, examples of which are described in greater detail below.

In an embodiment, each of the device locations 330A, 330B and 330C includes a lower set of nanowires 304A, 304B and 304C, and an upper set of nanowires 314A, 314B and 314C provided as a vertical stack. A dielectric nanowire cap layer 314D is included over each of the sets of nanowires, examples the formation of which are described below. As explained in greater detail in other embodiments described below, channel regions of the lower set of nanowires 304A, 304B and 304C and the upper set of nanowires 314A, 314B and 314C may be exposed during a replacement gate process during which an open trench 308A is formed to expose the channel regions. Trench 308A may be separated from other replacement gate trenches (e.g., 308B and 308C) by sidewalls spacers 310A, trench fill dielectric layers 310B and hardmask caps or helmets 310C.

Referring to FIG. 3B, the lower set of nanowires 304A, 304B and 304C of device locations 330A and 330B are depopulated in a first oxidation process. The lower set of nanowires 304A, 304B and 304C of device location 330C are not depopulated. In an embodiment, the lower set of nanowires 304A, 304B and 304C of device locations 330A and 330B are depopulated using an oxidation catalyst layer that is first formed on all nanowires and then patterned to confine the oxidation catalyst layer to lower set of nanowires 304A, 304B and 304C of device locations 330A and 330B. A first oxidation process is then performed to form oxide nanowires 350A, 350B and 350C, such as the oxidation process described in association with FIG. 2 . A lower set of active nanowires 304A, 304B and 304C are retained in device location 330C.

Referring to FIG. 3C, bottommost nanowires 314A, 314B and 314C of the upper set of nanowires of device locations 330A and 330C are depopulated in a second oxidation process. The bottommost nanowires 314A, 314B and 314C of the upper set of nanowires of device location 330B are not depopulated. In an embodiment, the bottommost nanowires 314A, 314B and 314C of the upper set of nanowires of device locations 330A and 330C are depopulated using an oxidation catalyst layer that is first formed on all nanowires of the upper sets of nanowires and then patterned to confine the oxidation catalyst layer to the bottommost nanowires 314A, 314B and 314C of the upper set of nanowires of device locations 330A and 330C.

In an embodiment, the bottom sets of nanowires previously subjected to the first oxidation process are blocked by a lower masking layer to enable a second selective oxidation process to be confined to the upper sets of nanowires, allowing for a second “bottom-up” oxidation depopulation approach. A second oxidation process is then performed to form oxide nanowires 360A, 360B and 360C, such as the oxidation process described in association with FIG. 2 . It is to be appreciated that the specific example of depopulated nanowires versus active nanowires, any suitable number of nanowires may be retained or oxidized to form oxide nanowires using a first oxidation depopulation approach for lower sets of nanowires, and then using a second oxidation depopulation approach for upper sets of nanowires.

Referring to FIG. 3D, a permanent gate structure may be fabricated in trench 308A. In one exemplary embodiment, the permanent gate structure includes a lower gate dielectric 370 and lower P-type gate electrode 372 thereon, and an upper gate dielectric 370 and upper N-type gate electrode 374 thereon. In another exemplary embodiment, the permanent gate structure includes a lower gate dielectric and lower N-type gate electrode thereon, and an upper gate dielectric and upper P-type gate electrode thereon. In an embodiment, the permanent gate structure is formed around all nanowire/nanoribbon (NW/NR) channels, including the oxide NW/NR channels. In a particular such embodiment, the oxidation catalyst layer is not removed, and the remainder is included in the final structure. In other embodiments, however, the oxidation catalyst layer is removed prior to permanent gate structure fabrication.

With reference again to FIG. 3D, in accordance with an embodiment of the present disclosure, an integrated circuit structure includes a first vertical arrangement of nanowires (e.g., nanowires 350A, 350B and 350C of device location 308B). The first vertical arrangement of nanowires has one or more oxide nanowires (e.g., nanowires 350A, 350B and 350C). A first gate stack (e.g., 370/372) is over the first vertical arrangement of nanowires and around the one or more oxide nanowires of the first vertical arrangement of nanowires. A second vertical arrangement of nanowires is above the first vertical arrangement of nanowires (e.g., nanowires 314A, 314B and 314C of device location 308B). The second vertical arrangement of nanowires has one or more active nanowires. A second gate stack is over the vertical arrangement of nanowires and around the one or more active nanowires of the second vertical arrangement of nanowires.

In an embodiment, the one or more oxide nanowires have an oxidation catalyst layer thereon, e.g., as a residual layer or artifact layer remaining from a multiple bottom-up channel depopulation process. In one embodiment, the oxidation catalyst layer includes aluminum oxide. In another embodiment, the oxidation catalyst layer includes lanthanum oxide.

In an embodiment, the integrated circuit structure includes epitaxial source or drain structures at ends of the first and second vertical arrangement of nanowires. In one such embodiment, the epitaxial source or drain structures are discrete epitaxial source or drain structures, structural examples of which are described below. In another such embodiment, the epitaxial source or drain structures are non-discrete epitaxial source or drain structures, structural examples of which are described below. In an embodiment, the first and second gate stacks have dielectric sidewall spacers, and the epitaxial source or drain structures are embedded epitaxial source or drain structures extending beneath the dielectric sidewall spacers of the gate stack, structural examples of which are described below.

In an embodiment, the integrated circuit structure further includes a pair of conductive contact structures coupled to the epitaxial source or drain structures. In one such embodiment, the pair of conductive contact structures is an asymmetric pair of conductive contact structures, structural examples of which are described below.

In an embodiment, the first vertical arrangement of nanowires is over a fin, structural examples of which are described below. In an embodiment, the first gate stack includes a first high-k gate dielectric layer and a first metal gate electrode, and the second gate stack includes a second high-k gate dielectric layer and a second metal gate electrode.

It is to be appreciated that embodiments described herein may be implemented to fabricate nanowire and/or nanoribbon structures having a different number of active wire/ribbon channels. It is to be appreciated that embodiments described herein may involve selective oxidation approaches to achieve such structures. Embodiments described herein may be implemented to enable the fabrication of nanowire/nanoribbon-based CMOS architectures.

With reference again to FIG. 3D, in accordance with an embodiment of the present disclosure, an integrated circuit structure includes a first vertical arrangement of nanowires (e.g., nanowires at device location 308B) and a second vertical arrangement of nanowires (e.g., nanowires at device location 308C). The first vertical arrangement of nanowires has an active uppermost nanowire (e.g., active nanowire 314C of device location 308B) and an oxide bottommost nanowire (e.g., oxide nanowire 304A of device location 308B). The second vertical arrangement of nanowires has an oxide uppermost nanowire (e.g., oxide nanowire 360C of device location 308C) and an active bottommost nanowire (e.g., active nanowire 304C of device location 308C), and the first and second vertical arrangements of nanowires having co-planar uppermost nanowires and co-planar bottommost nanowires. A first gate structure 370/372 is over the first vertical arrangement of nanowires. A second gate structure 370/372 is over the second vertical arrangement of nanowires.

In an embodiment, the nanowires of the first vertical arrangement of nanowires have a horizontal width the same as a horizontal width of the nanowires of the second vertical arrangement of nanowires. In an embodiment, the nanowires of the first vertical arrangement of nanowires have a horizontal width greater than a horizontal width of the nanowires of the second vertical arrangement of nanowires. In an embodiment, the nanowires of the first vertical arrangement of nanowires have a horizontal width less than a horizontal width of the nanowires of the second vertical arrangement of nanowires.

With reference again to FIG. 3D, in accordance with one or more embodiments of the present disclosure, all of the nanowire channels of the integrated circuit structure formed in device location 330A have been depopulated, e.g., to provide a “fully” depopulated structure in device location 330A. In one embodiment, the full depopulation is achieved using two successive bottom-up oxidation approaches. In an embodiment, the gate structure (e.g., 372/374) highlighted within the illustrated box 382 acts as a conductive via. In one embodiment, the conductive via is a front-to-back via.

Furthermore, in an embodiment, the substrate 302 of FIGS. 3A-3C is replaced with a backside interconnect layer. The backside interconnect layer may include conductive lines 394 and conductive vias 396 in a dielectric layer 392 formed on an etch stop layer 398. In one embodiment, the substrate portion of FIG. 3C is removed in a backside grind process, examples of which are described in greater detail below, and then the interconnect layer is formed thereon. Additionally, the structure in FIG. 3D includes front side gate contacts or vias 380A, 380B and 380C, which may include an insulating cap layer 390 formed thereon.

With reference again to FIG. 3D, in an embodiment, an integrated circuit structure 330A includes a vertical arrangement of nanowires 350A, 350B, 350C, 360A, 360B, and 360C. All nanowires 350A, 350B, 350C, 360A, 360B, and 360C of the vertical arrangement of nanowires are oxide nanowires. A gate stack 370/372/374 is over the vertical arrangement of nanowires, around each of the oxide nanowires 350A, 350B, 350C, 360A, 360B, and 360C. The gate stack 370/372/374 includes a conductive gate electrode 372/374.

In an embodiment, the integrated circuit structure 330A further includes a gate contact 380A above the vertical arrangement of nanowires 350A, 350B, 350C, 360A, 360B, and 360C. The gate contact 380A is in contact with a top surface of the conductive gate electrode 372/374. An interconnect structure 394/396 is below the vertical arrangement of nanowires 350A, 350B, 350C, 360A, 360B, and 360C. A conductive via 396 of the interconnect structure 394/396 is in contact with a bottom surface of the conductive gate electrode 372/374. The conductive gate electrode 372/374 acts as a conductive via between the gate contact 380A and the interconnect structure 394/396. In a particular embodiment, the oxide nanowires 350A, 350B, 350C, 360A, 360B, and 360C of the vertical arrangement of nanowires have an oxidation catalyst layer thereon.

In accordance with an embodiment of the present disclosure, the fabrication of gate regions that become front-to-back vias do not necessarily require dedicated lithographic patterning to define the via. For example, in one embodiment, full depopulation in select locations is achieved by combining other depopulation operations. As described herein, such front-to-back via fabrication may also need not involve an aggressive etch to remove the depopulated channels such that the surrounding materials (e.g., gate spacer, isolation walls, etc.) are not eroded. In some embodiments, however, the depopulated channels are selectively removed in the front-to-back via regions prior to gate metallization using a less-aggressive etch than may otherwise be associated with the opening of similar vias.

As mentioned above, nanowire release processing may be performed through a replacement gate trench. Examples of such release processes are described below. Additionally, in another aspect, backend (BE) interconnect scaling can result in lower performance and higher manufacturing cost due to patterning complexity. Embodiments described herein may be implemented to enable front and backside interconnect integration for nanowire transistors. Embodiments described herein may provide an approach to achieve a relatively wider interconnect pitch. The result may be improved product performance and lower patterning costs. Embodiments may be implemented to enable robust functionality of scaled nanowire or nanoribbon transistors with low power and high performance.

One or more embodiments described herein are directed dual epitaxial (EPI) connections for nanowire or nanoribbon transistors using partial source or drain (SD) and asymmetric trench contact (TCN) depth. In an embodiment, an integrated circuit structure is fabricated by forming source-drain openings of nanowire/nanoribbon transistors which are partially filled with SD epitaxy. A remainder of the opening is filled with a conductive material. Deep trench formation on one of the source or drain side enables direct contact to a backside interconnect level.

In an exemplary process flow, FIGS. 4A-4J illustrates cross-sectional views of various operations in a method of fabricating a gate-all-around integrated circuit structure, in accordance with an embodiment of the present disclosure.

Referring to FIG. 4A, a method of fabricating an integrated circuit structure includes forming a starting stack 400 which includes alternating silicon germanium layer 404 and silicon layers 406 above a fin 402, such as a silicon fin. The silicon layers 406 may be referred to as a vertical arrangement of silicon nanowires. A protective cap 408 may be formed above the alternating silicon germanium layer 404 and silicon layers 406, as is depicted.

Referring to FIG. 4B, a gate stack 410 is formed over the vertical arrangement of nanowires 406. Portions of the vertical arrangement of nanowires 406 are then released by removing portions of the silicon germanium layer 404 to provide recessed silicon germanium layers 404′ and cavities 412, as is depicted in FIG. 4C.

It is to be appreciated that the structure of FIG. 4C may be fabricated to completion without first performing the deep etch and asymmetric contact processing described below in association with FIG. 4D. In either case (e.g., with or without asymmetric contact processing), in an embodiment, a fabrication process involves use of a process scheme that provides a gate-all-around integrated circuit structure having a depopulated channel structure, examples of which are described above in association with FIGS. 2 and 3A-3D.

Referring to FIG. 4D, upper gate spacers 414 are formed at sidewalls of the gate structure 410. Cavity spacers 416 are formed in the cavities 412 beneath the upper gate spacers 414. A deep trench contact etch is then performed to form trenches 418 and to formed recessed nanowires 406′. A sacrificial material 420 is then formed in the trenches 418, as is depicted in FIG. 4E.

Referring to FIG. 4F, a first epitaxial source or drain structure (e.g., left-hand features 422) is formed at a first end of the vertical arrangement of nanowires 406′. A second epitaxial source or drain structure (e.g., right-hand features 422) is formed at a second end of the vertical arrangement of nanowires 406′. An inter-layer dielectric (ILD) material 424 is then formed at the sides of the gate electrode 410 and adjacent the source or drain structures 422, as is depicted in FIG. 4G.

Referring to FIG. 4H, a replacement gate process is used to form a permanent gate dielectric 428 and a permanent gate electrode 426. In an embodiment, subsequent to removal of gate structure 410 and form a permanent gate dielectric 428 and a permanent gate electrode 426, the recessed silicon germanium layers 404′ are removed to leave upper active nanowires or nanoribbons 406′. In an embodiment, the recessed silicon germanium layers 404′ are removed selectively with a wet etch that selectively removes the silicon germanium while not etching the silicon layers. Etch chemistries such as carboxylic acid/nitric acid/HF chemistry, and citric acid/nitric acid/HF, for example, may be utilized to selectively etch the silicon germanium. Halide-based dry etches or plasma-enhanced vapor etches may also be used to achieve the embodiments herein.

Referring again to FIG. 4H, one or more of the bottommost nanowires or nanoribbons 406′ is then oxidized to form one or more oxide nanowire or nanoribbons 499, e.g., by an approach described in association with FIGS. 2 and 3A-3D. The permanent gate dielectric 428 and a permanent gate electrode 426 is then formed to surround the nanowires or nanoribbons 406′ and the one or more oxide nanowire or nanoribbons 499.

Referring to FIG. 4I, the ILD material 424 is then removed. The sacrificial material 420 is then removed from one of the source drain locations (e.g., right-hand side) to form trench 432, but is not removed from the other of the source drain locations to form trench 430.

Referring to FIG. 4J, a first conductive contact structure 434 is formed coupled to the first epitaxial source or drain structure (e.g., left-hand features 422). A second conductive contact structure 436 is formed coupled to the second epitaxial source or drain structure (e.g., right-hand features 422). The second conductive contact structure 436 is formed deeper along the fin 402 than the first conductive contact structure 434. In an embodiment, although not depicted in FIG. 4J, the method further includes forming an exposed surface of the second conductive contact structure 436 at a bottom of the fin 402.

In an embodiment, the second conductive contact structure 436 is deeper along the fin 402 than the first conductive contact structure 434, as is depicted. In one such embodiment, the first conductive contact structure 434 is not along the fin 402, as is depicted. In another such embodiment, not depicted, the first conductive contact structure 434 is partially along the fin 402.

In an embodiment, the second conductive contact structure 434 is along an entirety of the fin 402. In an embodiment, although not depicted, in the case that the bottom of the fin 402 is exposed by a backside substrate removal process, the second conductive contact structure 434 has an exposed surface at a bottom of the fin 402.

In another aspect, in order to enable access to both conductive contact structures of a pair of asymmetric source and drain contact structures, integrated circuit structures described herein may be fabricated using a backside reveal of front-side structures fabrication approach. In some exemplary embodiments, reveal of the backside of a transistor or other device structure entails wafer-level backside processing. In contrast to a conventional through-Silicon via TSV-type technology, a reveal of the backside of a transistor as described herein may be performed at the density of the device cells, and even within sub-regions of a device. Furthermore, such a reveal of the backside of a transistor may be performed to remove substantially all of a donor substrate upon which a device layer was disposed during front-side device processing. As such, a microns-deep TSV becomes unnecessary with the thickness of semiconductor in the device cells following a reveal of the backside of a transistor potentially being only tens or hundreds of nanometers.

Reveal techniques described herein may enable a paradigm shift from “bottom-up” device fabrication to “center-out” fabrication, where the “center” is any layer that is employed in front-side fabrication, revealed from the backside, and again employed in backside fabrication. Processing of both a front side and revealed backside of a device structure may address many of the challenges associated with fabricating 3D ICs when primarily relying on front-side processing.

A reveal of the backside of a transistor approach may be employed for example to remove at least a portion of a carrier layer and intervening layer of a donor-host substrate assembly. The process flow begins with an input of a donor-host substrate assembly. A thickness of a carrier layer in the donor-host substrate is polished (e.g., CMP) and/or etched with a wet or dry (e.g., plasma) etch process. Any grind, polish, and/or wet/dry etch process known to be suitable for the composition of the carrier layer may be employed. For example, where the carrier layer is a group IV semiconductor (e.g., silicon) a CMP slurry known to be suitable for thinning the semiconductor may be employed. Likewise, any wet etchant or plasma etch process known to be suitable for thinning the group IV semiconductor may also be employed.

In some embodiments, the above is preceded by cleaving the carrier layer along a fracture plane substantially parallel to the intervening layer. The cleaving or fracture process may be utilized to remove a substantial portion of the carrier layer as a bulk mass, reducing the polish or etch time needed to remove the carrier layer. For example, where a carrier layer is 400-900 μm in thickness, 100-700 μm may be cleaved off by practicing any blanket implant known to promote a wafer-level fracture. In some exemplary embodiments, a light element (e.g., H, He, or Li) is implanted to a uniform target depth within the carrier layer where the fracture plane is desired. Following such a cleaving process, the thickness of the carrier layer remaining in the donor-host substrate assembly may then be polished or etched to complete removal. Alternatively, where the carrier layer is not fractured, the grind, polish and/or etch operation may be employed to remove a greater thickness of the carrier layer.

Next, exposure of an intervening layer is detected. Detection is used to identify a point when the backside surface of the donor substrate has advanced to nearly the device layer. Any endpoint detection technique known to be suitable for detecting a transition between the materials employed for the carrier layer and the intervening layer may be practiced. In some embodiments, one or more endpoint criteria are based on detecting a change in optical absorbance or emission of the backside surface of the donor substrate during the polishing or etching performed. In some other embodiments, the endpoint criteria are associated with a change in optical absorbance or emission of byproducts during the polishing or etching of the donor substrate backside surface. For example, absorbance or emission wavelengths associated with the carrier layer etch byproducts may change as a function of the different compositions of the carrier layer and intervening layer. In other embodiments, the endpoint criteria are associated with a change in mass of species in byproducts of polishing or etching the backside surface of the donor substrate. For example, the byproducts of processing may be sampled through a quadrupole mass analyzer and a change in the species mass may be correlated to the different compositions of the carrier layer and intervening layer. In another exemplary embodiment, the endpoint criteria is associated with a change in friction between a backside surface of the donor substrate and a polishing surface in contact with the backside surface of the donor substrate.

Detection of the intervening layer may be enhanced where the removal process is selective to the carrier layer relative to the intervening layer as non-uniformity in the carrier removal process may be mitigated by an etch rate delta between the carrier layer and intervening layer. Detection may even be skipped if the grind, polish and/or etch operation removes the intervening layer at a rate sufficiently below the rate at which the carrier layer is removed. If an endpoint criteria is not employed, a grind, polish and/or etch operation of a predetermined fixed duration may stop on the intervening layer material if the thickness of the intervening layer is sufficient for the selectivity of the etch. In some examples, the carrier etch rate:intervening layer etch rate is 3:1-10:1, or more.

Upon exposing the intervening layer, at least a portion of the intervening layer may be removed. For example, one or more component layers of the intervening layer may be removed. A thickness of the intervening layer may be removed uniformly by a polish, for example. Alternatively, a thickness of the intervening layer may be removed with a masked or blanket etch process. The process may employ the same polish or etch process as that employed to thin the carrier, or may be a distinct process with distinct process parameters. For example, where the intervening layer provides an etch stop for the carrier removal process, the latter operation may employ a different polish or etch process that favors removal of the intervening layer over removal of the device layer. Where less than a few hundred nanometers of intervening layer thickness is to be removed, the removal process may be relatively slow, optimized for across-wafer uniformity, and more precisely controlled than that employed for removal of the carrier layer. A CMP process employed may, for example employ a slurry that offers very high selectively (e.g., 100:1-300:1, or more) between semiconductor (e.g., silicon) and dielectric material (e.g., SiO) surrounding the device layer and embedded within the intervening layer, for example, as electrical isolation between adjacent device regions.

For embodiments where the device layer is revealed through complete removal of the intervening layer, backside processing may commence on an exposed backside of the device layer or specific device regions there in. In some embodiments, the backside device layer processing includes a further polish or wet/dry etch through a thickness of the device layer disposed between the intervening layer and a device region previously fabricated in the device layer, such as a source or drain region.

In some embodiments where the carrier layer, intervening layer, or device layer backside is recessed with a wet and/or plasma etch, such an etch may be a patterned etch or a materially selective etch that imparts significant non-planarity or topography into the device layer backside surface. As described further below, the patterning may be within a device cell (i.e., “intra-cell” patterning) or may be across device cells (i.e., “inter-cell” patterning). In some patterned etch embodiments, at least a partial thickness of the intervening layer is employed as a hard mask for backside device layer patterning. Hence, a masked etch process may preface a correspondingly masked device layer etch.

The above described processing scheme may result in a donor-host substrate assembly that includes IC devices that have a backside of an intervening layer, a backside of the device layer, and/or backside of one or more semiconductor regions within the device layer, and/or front-side metallization revealed. Additional backside processing of any of these revealed regions may then be performed during downstream processing.

It is to be appreciated that the structures resulting from the above exemplary processing schemes may be used in a same or similar form for subsequent processing operations to complete device fabrication, such as CMOS, PMOS and/or NMOS device fabrication. As an example of a completed device, FIG. 5 illustrates a cross-sectional view of a non-planar integrated circuit structure as taken along a gate line, in accordance with an embodiment of the present disclosure.

Referring to FIG. 5 , a semiconductor structure or device 500 includes a non-planar active region (e.g., a fin structure including protruding fin portion 504 and sub-fin region 505) within a trench isolation region 506. In an embodiment, instead of a solid fin, the non-planar active region is separated into nanowires (such as nanowires 504A and 504B) above sub-fin region 505, as is represented by the dashed lines. In either case, for ease of description for non-planar integrated circuit structure 500, a non-planar active region 504 is referenced below as a protruding fin portion. In an embodiment, a fabrication process involves use of a process scheme that provides active regions 504 as a depopulated channel structure, examples of which are described above in association with FIGS. 2 and 3A-3D. For example, in one embodiment, lower nanowires 504B are oxide nanowires, and upper nanowires 504A are active nanowires. In one embodiment, lower oxide nanowires 504B include an oxidation catalyst layer thereon.

A gate line 508 is disposed over the protruding portions 504 of the non-planar active region (including, if applicable, surrounding nanowires 504A and 504B), as well as over a portion of the trench isolation region 506. As shown, gate line 508 includes a gate electrode 550 and a gate dielectric layer 552. In one embodiment, gate line 508 may also include a dielectric cap layer 554. A gate contact 514, and overlying gate contact via 516 are also seen from this perspective, along with an overlying metal interconnect 560, all of which are disposed in inter-layer dielectric stacks or layers 570. Also seen from the perspective of FIG. 5 , the gate contact 514 is, in one embodiment, disposed over trench isolation region 506, but not over the non-planar active regions.

In an embodiment, the semiconductor structure or device 500 is a non-planar device such as, but not limited to, a fin-FET device, a tri-gate device, a nanoribbon device, or a nano-wire device. In such an embodiment, a corresponding semiconducting channel region is composed of or is formed in a three-dimensional body. In one such embodiment, the gate electrode stacks of gate lines 508 surround at least a top surface and a pair of sidewalls of the three-dimensional body.

As is also depicted in FIG. 5 , in an embodiment, an interface 580 exists between a protruding fin portion 504 and sub-fin region 505. The interface 580 can be a transition region between a doped sub-fin region 505 and a lightly or undoped upper fin portion 504. In one such embodiment, each fin is approximately 10 nanometers wide or less, and sub-fin dopants are supplied from an adjacent solid state doping layer at the sub-fin location. In a particular such embodiment, each fin is less than 10 nanometers wide.

Although not depicted in FIG. 5 , it is to be appreciated that source or drain regions of or adjacent to the protruding fin portions 504 are on either side of the gate line 508, i.e., into and out of the page. In one embodiment, the source or drain regions are doped portions of original material of the protruding fin portions 504. In another embodiment, the material of the protruding fin portions 504 is removed and replaced with another semiconductor material, e.g., by epitaxial deposition to form discrete epitaxial nubs or non-discrete epitaxial structures. In either embodiment, the source or drain regions may extend below the height of dielectric layer of trench isolation region 506, i.e., into the sub-fin region 505. In accordance with an embodiment of the present disclosure, the more heavily doped sub-fin regions, i.e., the doped portions of the fins below interface 580, inhibits source to drain leakage through this portion of the bulk semiconductor fins. In an embodiment, the source and drain structures are N-type epitaxial source and drain structures, both including phosphorous dopant impurity atoms. In accordance with one or more embodiments of the present disclosure, the source and drain regions have associated asymmetric source and drain contact structures, as described above in association with FIG. 4J.

With reference again to FIG. 5 , in an embodiment, fins 504/505 (and, possibly nanowires 504A and 504B) are composed of a crystalline silicon, silicon/germanium or germanium layer doped with a charge carrier, such as but not limited to phosphorus, arsenic, boron or a combination thereof. In one embodiment, the concentration of silicon atoms is greater than 97%. In another embodiment, fins 504/505 are composed of a group III-V material, such as, but not limited to, gallium nitride, gallium phosphide, gallium arsenide, indium phosphide, indium antimonide, indium gallium arsenide, aluminum gallium arsenide, indium gallium phosphide, or a combination thereof. Trench isolation region 506 may be composed of a dielectric material such as, but not limited to, silicon dioxide, silicon oxy-nitride, silicon nitride, or carbon-doped silicon nitride.

Gate line 508 may be composed of a gate electrode stack which includes a gate dielectric layer 552 and a gate electrode layer 550. In an embodiment, the gate electrode of the gate electrode stack is composed of a metal gate and the gate dielectric layer is composed of a high-K material. For example, in one embodiment, the gate dielectric layer is composed of a material such as, but not limited to, hafnium oxide, hafnium oxy-nitride, hafnium silicate, lanthanum oxide, zirconium oxide, zirconium silicate, tantalum oxide, barium strontium titanate, barium titanate, strontium titanate, yttrium oxide, aluminum oxide, lead scandium tantalum oxide, lead zinc niobate, or a combination thereof. Furthermore, a portion of gate dielectric layer may include a layer of native oxide formed from the top few layers of the protruding fin portions 504. In an embodiment, the gate dielectric layer is composed of a top high-k portion and a lower portion composed of an oxide of a semiconductor material. In one embodiment, the gate dielectric layer is composed of a top portion of hafnium oxide and a bottom portion of silicon dioxide or silicon oxy-nitride. In some implementations, a portion of the gate dielectric is a “U”-shaped structure that includes a bottom portion substantially parallel to the surface of the substrate and two sidewall portions that are substantially perpendicular to the top surface of the substrate.

In one embodiment, the gate electrode is composed of a metal layer such as, but not limited to, metal nitrides, metal carbides, metal silicides, metal aluminides, hafnium, zirconium, titanium, tantalum, aluminum, ruthenium, palladium, platinum, cobalt, nickel or conductive metal oxides. In a specific embodiment, the gate electrode is composed of a non-workfunction-setting fill material formed above a metal workfunction-setting layer. The gate electrode layer may consist of a P-type workfunction metal or an N-type workfunction metal, depending on whether the transistor is to be a PMOS or an NMOS transistor. In some implementations, the gate electrode layer may consist of a stack of two or more metal layers, where one or more metal layers are workfunction metal layers and at least one metal layer is a conductive fill layer. For a PMOS transistor, metals that may be used for the gate electrode include, but are not limited to, ruthenium, palladium, platinum, cobalt, nickel, and conductive metal oxides, e.g., ruthenium oxide. A P-type metal layer will enable the formation of a PMOS gate electrode with a workfunction that is between about 4.9 eV and about 5.2 eV. For an NMOS transistor, metals that may be used for the gate electrode include, but are not limited to, hafnium, zirconium, titanium, tantalum, aluminum, alloys of these metals, and carbides of these metals such as hafnium carbide, zirconium carbide, titanium carbide, tantalum carbide, and aluminum carbide. An N-type metal layer will enable the formation of an NMOS gate electrode with a workfunction that is between about 3.9 eV and about 4.2 eV. In some implementations, the gate electrode may consist of a “U”-shaped structure that includes a bottom portion substantially parallel to the surface of the substrate and two sidewall portions that are substantially perpendicular to the top surface of the substrate. In another implementation, at least one of the metal layers that form the gate electrode may simply be a planar layer that is substantially parallel to the top surface of the substrate and does not include sidewall portions substantially perpendicular to the top surface of the substrate. In further implementations of the disclosure, the gate electrode may consist of a combination of U-shaped structures and planar, non-U-shaped structures. For example, the gate electrode may consist of one or more U-shaped metal layers formed atop one or more planar, non-U-shaped layers.

Spacers associated with the gate electrode stacks may be composed of a material suitable to ultimately electrically isolate, or contribute to the isolation of, a permanent gate structure from adjacent conductive contacts, such as self-aligned contacts. For example, in one embodiment, the spacers are composed of a dielectric material such as, but not limited to, silicon dioxide, silicon oxy-nitride, silicon nitride, or carbon-doped silicon nitride.

Gate contact 514 and overlying gate contact via 516 may be composed of a conductive material. In an embodiment, one or more of the contacts or vias are composed of a metal species. The metal species may be a pure metal, such as tungsten, nickel, or cobalt, or may be an alloy such as a metal-metal alloy or a metal-semiconductor alloy (e.g., such as a silicide material).

In an embodiment (although not shown), a contact pattern which is essentially perfectly aligned to an existing gate pattern 508 is formed while eliminating the use of a lithographic step with exceedingly tight registration budget. In an embodiment, the contact pattern is a vertically asymmetric contact pattern, such as described in association with FIG. 4J. In other embodiments, all contacts are front side connected and are not asymmetric. In one such embodiment, the self-aligned approach enables the use of intrinsically highly selective wet etching (e.g., versus conventionally implemented dry or plasma etching) to generate contact openings. In an embodiment, a contact pattern is formed by utilizing an existing gate pattern in combination with a contact plug lithography operation. In one such embodiment, the approach enables elimination of the need for an otherwise critical lithography operation to generate a contact pattern, as used in conventional approaches. In an embodiment, a trench contact grid is not separately patterned, but is rather formed between poly (gate) lines. For example, in one such embodiment, a trench contact grid is formed subsequent to gate grating patterning but prior to gate grating cuts.

In an embodiment, providing structure 500 involves fabrication of the gate stack structure 508 by a replacement gate process. In such a scheme, dummy gate material such as polysilicon or silicon nitride pillar material, may be removed and replaced with permanent gate electrode material. In one such embodiment, a permanent gate dielectric layer is also formed in this process, as opposed to being carried through from earlier processing. In an embodiment, dummy gates are removed by a dry etch or wet etch process. In one embodiment, dummy gates are composed of polycrystalline silicon or amorphous silicon and are removed with a dry etch process including use of SF₆. In another embodiment, dummy gates are composed of polycrystalline silicon or amorphous silicon and are removed with a wet etch process including use of aqueous NH₄OH or tetramethylammonium hydroxide. In one embodiment, dummy gates are composed of silicon nitride and are removed with a wet etch including aqueous phosphoric acid.

Referring again to FIG. 5 , the arrangement of semiconductor structure or device 500 places the gate contact over isolation regions. Such an arrangement may be viewed as inefficient use of layout space. In another embodiment, however, a semiconductor device has contact structures that contact portions of a gate electrode formed over an active region, e.g., over a sub-fin 505, and in a same layer as a trench contact via.

It is to be appreciated that not all aspects of the processes described above need be practiced to fall within the spirit and scope of embodiments of the present disclosure. Also, the processes described herein may be used to fabricate one or a plurality of semiconductor devices. The semiconductor devices may be transistors or like devices. For example, in an embodiment, the semiconductor devices are a metal-oxide semiconductor (MOS) transistors for logic or memory, or are bipolar transistors. Also, in an embodiment, the semiconductor devices have a three-dimensional architecture, such as a nanowire device, a nanoribbon device, a gate-all-around (GAA) device, a tri-gate device, an independently accessed double gate device, or a FIN-FET. One or more embodiments may be particularly useful for fabricating semiconductor devices at a sub-10 nanometer (10 nm) technology node.

In an embodiment, as used throughout the present description, interlayer dielectric (ILD) material is composed of or includes a layer of a dielectric or insulating material. Examples of suitable dielectric materials include, but are not limited to, oxides of silicon (e.g., silicon dioxide (SiO₂)), doped oxides of silicon, fluorinated oxides of silicon, carbon doped oxides of silicon, various low-k dielectric materials known in the arts, and combinations thereof. The interlayer dielectric material may be formed by conventional techniques, such as, for example, chemical vapor deposition (CVD), physical vapor deposition (PVD), or by other deposition methods.

In an embodiment, as is also used throughout the present description, metal lines or interconnect line material (and via material) is composed of one or more metal or other conductive structures. A common example is the use of copper lines and structures that may or may not include barrier layers between the copper and surrounding ILD material. As used herein, the term metal includes alloys, stacks, and other combinations of multiple metals. For example, the metal interconnect lines may include barrier layers (e.g., layers including one or more of Ta, TaN, Ti or TiN), stacks of different metals or alloys, etc. Thus, the interconnect lines may be a single material layer, or may be formed from several layers, including conductive liner layers and fill layers. Any suitable deposition process, such as electroplating, chemical vapor deposition or physical vapor deposition, may be used to form interconnect lines. In an embodiment, the interconnect lines are composed of a conductive material such as, but not limited to, Cu, Al, Ti, Zr, Hf, V, Ru, Co, Ni, Pd, Pt, W, Ag, Au or alloys thereof. The interconnect lines are also sometimes referred to in the art as traces, wires, lines, metal, or simply interconnect.

In an embodiment, as is also used throughout the present description, hardmask materials, capping layers, or plugs are composed of dielectric materials different from the interlayer dielectric material. In one embodiment, different hardmask, capping or plug materials may be used in different regions so as to provide different growth or etch selectivity to each other and to the underlying dielectric and metal layers. In some embodiments, a hardmask layer, capping or plug layer includes a layer of a nitride of silicon (e.g., silicon nitride) or a layer of an oxide of silicon, or both, or a combination thereof. Other suitable materials may include carbon-based materials. Other hardmask, capping or plug layers known in the arts may be used depending upon the particular implementation. The hardmask, capping or plug layers maybe formed by CVD, PVD, or by other deposition methods.

In an embodiment, as is also used throughout the present description, lithographic operations are performed using 193 nm immersion litho (i193), EUV and/or EBDW lithography, or the like. A positive tone or a negative tone resist may be used. In one embodiment, a lithographic mask is a trilayer mask composed of a topographic masking portion, an anti-reflective coating (ARC) layer, and a photoresist layer. In a particular such embodiment, the topographic masking portion is a carbon hardmask (CHM) layer and the anti-reflective coating layer is a silicon ARC layer.

In another aspect, one or more embodiments are directed to neighboring semiconductor structures or devices separated by self-aligned gate endcap (SAGE) structures. Particular embodiments may be directed to integration of multiple width (multi-Wsi) nanowires and nanoribbons in a SAGE architecture and separated by a SAGE wall. In an embodiment, nanowires/nanoribbons are integrated with multiple Wsi in a SAGE architecture portion of a front end process flow. Such a process flow may involve integration of nanowires and nanoribbons of different Wsi to provide robust functionality of next generation transistors with low power and high performance. Associated epitaxial source or drain regions may be embedded (e.g., portions of nanowires removed and then source or drain (S/D) growth is performed) or formed by vertical merging (e.g., epitaxial regions are formed around existing wires), as described in greater detail below in association with FIGS. 9A-9E.

To provide further context, advantages of a self-aligned gate endcap (SAGE) architecture may include the enabling of higher layout density and, in particular, scaling of diffusion to diffusion spacing. To provide illustrative comparison, FIG. 6 illustrates cross-sectional views taken through nanowires and fins for a non-endcap architecture (left-hand side (a)) versus a self-aligned gate endcap (SAGE) architecture (right-hand side (b)), in accordance with an embodiment of the present disclosure.

Referring to the left-hand side (a) of FIG. 6 , an integrated circuit structure 600 includes a substrate 602 having sub-fins 604 protruding therefrom within an isolation structure 608 laterally surrounding the sub-fins 604. Corresponding nanowires 649 and 605 are over the sub-fins 604. In one embodiment, lower nanowires 649 are oxide nanowires, and upper nanowires 605 are active nanowires. In one embodiment, lower oxide nanowires 649 include an oxidation catalyst layer thereon. A gate structure may be formed over the integrated circuit structure 600 to fabricate a device. However, breaks in such a gate structure may be accommodated for by increasing the spacing between sub-fin 604/nanowire 649/605 pairings.

By contrast, referring to the right-hand side (b) of FIG. 6 , an integrated circuit structure 650 includes a substrate 652 having sub-fins 654 protruding therefrom within an isolation structure 658 laterally surrounding the sub-fins 654. Corresponding nanowires 699 and 655 are over the sub-fins 654. In one embodiment, lower nanowires 699 are oxide nanowires, and upper nanowires 655 are active nanowires. In one embodiment, lower oxide nanowires 699 include an oxidation catalyst layer thereon. Isolating SAGE walls 660 are included within the isolation structure 658 and between adjacent sub-fin 654/nanowire 699/655 pairings. The distance between an isolating SAGE wall 660 and a nearest sub-fin 654/nanowire 699/655 pairings defines the gate endcap spacing 662. A gate structure may be formed over the integrated circuit structure 600, between insolating SAGE walls to fabricate a device. Breaks in such a gate structure are imposed by the isolating SAGE walls. Since the isolating SAGE walls 660 are self-aligned, restrictions from conventional approaches can be minimized to enable more aggressive diffusion to diffusion spacing. Furthermore, since gate structures include breaks at all locations, individual gate structure portions may be layer connected by local interconnects formed over the isolating SAGE walls 660. In an embodiment, as depicted, the SAGE walls 660 each include a lower dielectric portion and a dielectric cap on the lower dielectric portion, as is depicted.

In accordance with an embodiment of the present disclosure, a fabrication process for structures associated with FIG. 6 involves use of a process scheme that provides a gate-all-around integrated circuit structure having a depopulated channel structure, examples of which are described above in association with FIGS. 2 and 3A-3D.

A self-aligned gate endcap (SAGE) processing scheme involves the formation of gate/trench contact endcaps self-aligned to fins without requiring an extra length to account for mask mis-registration. Thus, embodiments may be implemented to enable shrinking of transistor layout area. Embodiments described herein may involve the fabrication of gate endcap isolation structures, which may also be referred to as gate walls, isolation gate walls or self-aligned gate endcap (SAGE) walls.

In an exemplary processing scheme for structures having SAGE walls separating neighboring devices, FIG. 7 illustrate cross-sectional views representing various operations in a method of fabricating a self-aligned gate endcap (SAGE) structure with gate-all-around devices, in accordance with an embodiment of the present disclosure.

Referring to part (a) of FIG. 7 , a starting structure includes a nanowire patterning stack 704 above a substrate 702. A lithographic patterning stack 706 is formed above the nanowire patterning stack 704. The nanowire patterning stack 704 includes alternating silicon germanium layers 710 and silicon layers 712. A protective mask 714 is between the nanowire patterning stack 704 and the lithographic patterning stack 706. In one embodiment, the lithographic patterning stack 706 is trilayer mask composed of a topographic masking portion 720, an anti-reflective coating (ARC) layer 722, and a photoresist layer 724. In a particular such embodiment, the topographic masking portion 720 is a carbon hardmask (CHM) layer and the anti-reflective coating layer 722 is a silicon ARC layer.

Referring to part (b) of FIG. 7 , the stack of part (a) is lithographically patterned and then etched to provide an etched structure including a patterned substrate 702 and trenches 730.

Referring to part (c) of FIG. 7 , the structure of part (b) has an isolation layer 740 and a SAGE material 742 formed in trenches 730. The structure is then planarized to leave patterned topographic masking layer 720′ as an exposed upper layer.

Referring to part (d) of FIG. 7 , the isolation layer 740 is recessed below an upper surface of the patterned substrate 702, e.g., to define a protruding fin portion and to provide a trench isolation structure 741 beneath SAGE walls 742.

Referring to part (e) of FIG. 7 , the silicon germanium layers 710 are removed at least in the channel region to release silicon nanowires 712A and 712B.

In accordance with an embodiment of the present disclosure, a fabrication process for structures associated with FIG. 7 involves use of a process scheme that provides a gate-all-around integrated circuit structure having a depopulated channel structure, examples of which are described above in association with FIGS. 2 and 3A-3D. For example, referring to part (e) of FIG. 7 , in an embodiment, nanowire 712B and nanoribbon 712A are an active nanowire and nanoribbon, respectively. In one such embodiment, nanowire 799B is an oxide nanowire, and nanoribbon 799A is an oxide nanoribbon, as is depicted. In another such embodiment, nanowire 799B is an oxide nanowire, and nanoribbon 799A is an active nanoribbon. In another such embodiment, nanowire 799B is an active nanowire, and nanoribbon 799A is an oxide nanoribbon. In any case, in an embodiment, an oxide nanowire or an oxide nanoribbon includes an oxidation catalyst layer thereon.

Subsequent to the formation of the structure of part (e) of FIG. 7 , one or more gate stacks may be formed around the active and oxide nanowires and/or nanoribbons, over protruding fins of substrate 702, and between SAGE walls 742. In one embodiment, prior to formation of the gate stacks, the remaining portion of protective mask 714 is removed. In another embodiment, the remaining portion of protective mask 714 is retained as an insulating fin hat as an artifact of the processing scheme.

Referring again to part (e) of FIG. 7 , it is to be appreciated that a channel view is depicted, with source or drain regions being locating into and out of the page. In an embodiment, the channel region including nanowires 712B has a width less than the channel region including nanowires 712A. Thus, in an embodiment, an integrated circuit structure includes multiple width (multi-Wsi) nanowires. Although structures of 712B and 712A may be differentiated as nanowires and nanoribbons, respectively, both such structures are typically referred to herein as nanowires. It is also to be appreciated that reference to or depiction of a fin/nanowire pair throughout may refer to a structure including a fin and one or more overlying nanowires (e.g., two overlying nanowires are shown in FIG. 7 ), where one or more bottom wires are oxidized for depopulation.

With reference again to part (e) of FIG. 7 and the subsequent description, in accordance with an embodiment of the present disclosure, an integrated circuit structure includes a first vertical arrangement of nanowires and a second vertical arrangement of nanowires above a substrate. The first vertical arrangement of nanowires has a greater number of active nanowires than the second vertical arrangement of nanowires. The first and second vertical arrangements of nanowires have co-planar uppermost nanowires and co-planar bottommost nanowires. The second vertical arrangement of nanowires has an oxide bottommost nanowire. A first gate stack is over the first vertical arrangement of nanowires. A second gate stack is over the second vertical arrangement of nanowires and around the oxide bottommost nanowire.

In an embodiment, the nanowires of the first vertical arrangement of nanowires have a horizontal width the same as a horizontal width of the nanowires of the second vertical arrangement of nanowires. In another embodiment, the nanowires of the first vertical arrangement of nanowires have a horizontal width greater than a horizontal width of the nanowires of the second vertical arrangement of nanowires. In another embodiment, the nanowires of the first vertical arrangement of nanowires have a horizontal width less than a horizontal width of the nanowires of the second vertical arrangement of nanowires.

To highlight an exemplary integrated circuit structure having three vertically arranged nanowires, FIG. 8A illustrates a three-dimensional cross-sectional view of a nanowire-based integrated circuit structure, in accordance with an embodiment of the present disclosure. FIG. 8B illustrates a cross-sectional source or drain view of the nanowire-based integrated circuit structure of FIG. 8A, as taken along the a-a′ axis. FIG. 8C illustrates a cross-sectional channel view of the nanowire-based integrated circuit structure of FIG. 8A, as taken along the b-b′ axis.

Referring to FIG. 8A, an integrated circuit structure 800 includes one or more vertically stacked nanowires (804 set) above a substrate 802. An optional fin between the bottommost nanowire and the substrate 802 is not depicted for the sake of emphasizing the nanowire portion for illustrative purposes. Embodiments herein are targeted at both single wire devices and multiple wire devices. As an example, a three nanowire-based devices having nanowires 804A, 804B and 804C is shown for illustrative purposes. For convenience of description, nanowire 804A is used as an example where description is focused on one of the nanowires. It is to be appreciated that where attributes of one nanowire are described, embodiments based on a plurality of nanowires may have the same or essentially the same attributes for each of the nanowires.

Each of the nanowires 804 includes a channel region 806 in the nanowire. The channel region 806 has a length (L). Referring to FIG. 8C, the channel region also has a perimeter (Pc) orthogonal to the length (L). Referring to both FIGS. 8A and 8C, a gate electrode stack 808 surrounds the entire perimeter (Pc) of each of the channel regions 806. The gate electrode stack 808 includes a gate electrode along with a gate dielectric layer between the channel region 806 and the gate electrode (not shown). In an embodiment, the channel region is discrete in that it is completely surrounded by the gate electrode stack 808 without any intervening material such as underlying substrate material or overlying channel fabrication materials. Accordingly, in embodiments having a plurality of nanowires 804, the channel regions 806 of the nanowires are also discrete relative to one another.

In accordance with an embodiment of the present disclosure, a fabrication process for structures associated with FIGS. 8A-8C involves use of a process scheme that provides a gate-all-around integrated circuit structure having a depopulated channel structure 806, examples of which are described above in association with FIGS. 2 and 3A-3D. For example, in one embodiment, nanowire 804A is an oxide nanowire. In another embodiment, both nanowire 804A and nanowire 804B are oxide nanowires. In one embodiment, an oxide nanowire includes an oxidation catalyst layer thereon.

Referring to both FIGS. 8A and 8B, integrated circuit structure 800 includes a pair of non-discrete source or drain regions 810/812. The pair of non-discrete source or drain regions 810/812 is on either side of the channel regions 806 of the plurality of vertically stacked nanowires 804. Furthermore, the pair of non-discrete source or drain regions 810/812 is adjoining for the channel regions 806 of the plurality of vertically stacked nanowires 804. In one such embodiment, not depicted, the pair of non-discrete source or drain regions 810/812 is directly vertically adjoining for the channel regions 806 in that epitaxial growth is on and between nanowire portions extending beyond the channel regions 806, where nanowire ends are shown within the source or drain structures. In another embodiment, as depicted in FIG. 8A, the pair of non-discrete source or drain regions 810/812 is indirectly vertically adjoining for the channel regions 806 in that they are formed at the ends of the nanowires and not between the nanowires.

In an embodiment, as depicted, the source or drain regions 810/812 are non-discrete in that there are not individual and discrete source or drain regions for each channel region 806 of a nanowire 804. Accordingly, in embodiments having a plurality of nanowires 804, the source or drain regions 810/812 of the nanowires are global or unified source or drain regions as opposed to discrete for each nanowire. In one embodiment, from a cross-sectional perspective orthogonal to the length of the discrete channel regions 806, each of the pair of non-discrete source or drain regions 810/812 is approximately rectangular in shape with a bottom tapered portion and a top vertex portion, as depicted in FIG. 8B. In other embodiments, however, the source or drain regions 810/812 of the nanowires are relatively larger yet discrete non-vertically merged epitaxial structures such as nubs described in association with FIGS. 4F-4J.

In accordance with an embodiment of the present disclosure, and as depicted in FIGS. 8A and 8B, integrated circuit structure 800 further includes a pair of contacts 814, each contact 814 on one of the pair of non-discrete source or drain regions 810/812. In one such embodiment, in a vertical sense, each contact 814 completely surrounds the respective non-discrete source or drain region 810/812. In another aspect, the entire perimeter of the non-discrete source or drain regions 810/812 may not be accessible for contact with contacts 814, and the contact 814 thus only partially surrounds the non-discrete source or drain regions 810/812, as depicted in FIG. 8B. In a contrasting embodiment, not depicted, the entire perimeter of the non-discrete source or drain regions 810/812, as taken along the a-a′ axis, is surrounded by the contacts 814. In accordance with an embodiment of the present disclosure, although not depicted, the pair of contacts 814 is an asymmetric pair of contacts, as described in association with FIG. 4J.

Referring to FIGS. 8B and 8C, the non-discrete source or drain regions 810/812 are global in the sense that a single unified feature is used as a source or drain region for a plurality (in this case, 3) of nanowires 804 and, more particularly, for more than one discrete channel region 806. In an embodiment, the pair of non-discrete source or drain regions 810/812 is composed of a semiconductor material different than the semiconductor material of the discrete channel regions 806, e.g., the pair of non-discrete source or drain regions 810/812 is composed of a silicon germanium while the discrete channel regions 806 are composed of silicon. In another embodiment, the pair of non-discrete source or drain regions 810/812 is composed of a semiconductor material the same or essentially the same as the semiconductor material of the discrete channel regions 806, e.g., both the pair of non-discrete source or drain regions 810/812 and the discrete channel regions 806 are composed of silicon.

Referring again to FIG. 8A, in an embodiment, integrated circuit structure 800 further includes a pair of spacers 816. As is depicted, outer portions of the pair of spacers 816 may overlap portions of the non-discrete source or drain regions 810/812, providing for “embedded” portions of the non-discrete source or drain regions 810/812 beneath the pair of spacers 816. As is also depicted, the embedded portions of the non-discrete source or drain regions 810/812 may not extend beneath the entirety of the pair of spacers 816.

Substrate 802 may be composed of a material suitable for integrated circuit structure fabrication. In one embodiment, substrate 802 includes a lower bulk substrate composed of a single crystal of a material which may include, but is not limited to, silicon, germanium, silicon-germanium or a III-V compound semiconductor material. An upper insulator layer composed of a material which may include, but is not limited to, silicon dioxide, silicon nitride or silicon oxy-nitride is on the lower bulk substrate. Thus, the structure 800 may be fabricated from a starting semiconductor-on-insulator substrate. Alternatively, the structure 800 is formed directly from a bulk substrate and local oxidation is used to form electrically insulative portions in place of the above described upper insulator layer. In another alternative embodiment, the structure 800 is formed directly from a bulk substrate and doping is used to form electrically isolated active regions, such as nanowires, thereon. In one such embodiment, the first nanowire (i.e., proximate the substrate) is in the form of an omega-FET type structure.

In an embodiment, the nanowires 804 may be sized as wires or ribbons, as described below, and may have squared-off or rounder corners. In an embodiment, the nanowires 804 are composed of a material such as, but not limited to, silicon, germanium, or a combination thereof. In one such embodiment, the nanowires are single-crystalline. For example, for a silicon nanowire 804, a single-crystalline nanowire may be based from a (100) global orientation, e.g., with a <100> plane in the z-direction. As described below, other orientations may also be considered. In an embodiment, the dimensions of the nanowires 804, from a cross-sectional perspective, are on the nano-scale. For example, in a specific embodiment, the smallest dimension of the nanowires 804 is less than approximately 20 nanometers. In an embodiment, the nanowires 804 are composed of a strained material, particularly in the channel regions 806.

Referring to FIG. 8C, in an embodiment, each of the channel regions 806 has a width (Wc) and a height (Hc), the width (Wc) approximately the same as the height (Hc). That is, in both cases, the channel regions 806 are square-like or, if corner-rounded, circle-like in cross-section profile. In another aspect, the width and height of the channel region need not be the same, such as the case for nanoribbbons as described throughout.

In another aspect, methods of fabricating a nanowire portion of a fin/nanowire integrated circuit structure are provided. For example, FIGS. 9A-9E illustrate three-dimensional cross-sectional views representing various operations in a method of fabricating a nanowire portion of a fin/nanowire structure, in accordance with an embodiment of the present disclosure.

A method of fabricating a nanowire integrated circuit structure may include forming a nanowire above a substrate. In a specific example showing the formation of two silicon nanowires, FIG. 9A illustrates a substrate 902 (e.g., composed of a bulk substrate silicon substrate 902A with an insulating silicon dioxide layer 902B there on) having a silicon layer 904/silicon germanium layer 906/silicon layer 908 stack thereon. It is to be understood that, in another embodiment, a silicon germanium layer/silicon layer/silicon germanium layer stack may be used to ultimately form two silicon germanium nanowires.

Referring to FIG. 9B, a portion of the silicon layer 904/silicon germanium layer 906/silicon layer 908 stack as well as a top portion of the silicon dioxide layer 902B is patterned into a fin-type structure 910, e.g., with a mask and plasma etch process. It is to be appreciated that, for illustrative purposes, the etch for FIG. 9B is shown as forming two silicon nanowire precursor portions. Although the etch is shown for ease of illustration as ending within a bottom isolation layer, more complex stacks are contemplated within the context of embodiments of the present disclosure. For example, the process may be applied to a nanowire/fin stack as described in association with FIG. 7 .

The method may also include forming a channel region in the nanowire, the channel region having a length and a perimeter orthogonal to the length. In a specific example showing the formation of three gate structures over the two silicon nanowires, FIG. 9C illustrates the fin-type structure 910 with three sacrificial gates 912A, 912B, and 912C thereon. In one such embodiment, the three sacrificial gates 912A, 912B, and 912C are composed of a sacrificial gate oxide layer 914 and a sacrificial polysilicon gate layer 916 which are blanket deposited and patterned with a plasma etch process.

Following patterning to form the three sacrificial gates 912A, 912B, and 912C, spacers may be formed on the sidewalls of the three sacrificial gates 912A, 912B, and 912C, doping may be performed (e.g., tip and/or source and drain type doping), and an interlayer dielectric layer may be formed to cover the three sacrificial gates 912A, 912B, and 912C. The interlayer dielectric layer may be polished to expose the three sacrificial gates 912A, 912B, and 912C for a replacement gate, or gate-last, process.

Referring to FIG. 9D, the three sacrificial gates 912A, 912B, and 912C are removed, leaving spacers 918 and a portion of the interlayer dielectric layer 920 remaining. Additionally, the portions of the silicon germanium layer 906 and the portion of the insulating silicon dioxide layer 902B of the fin structure 910 are removed in the regions originally covered by the three sacrificial gates 912A, 912B, and 912C. Discrete portions of the silicon layers 904 and 908 thus remain, as depicted in FIG. 9D.

The discrete portions of the silicon layers 904 and 908 shown in FIG. 9D will, in one embodiment, ultimately become channel regions in a nanowire-based device. Thus, at the process stage depicted in FIG. 9D, channel engineering or tuning may be performed. For example, in one embodiment, the discrete portions of the silicon layers 904 and 908 shown in FIG. 9D are thinned using oxidation and etch processes. Such an etch process may be performed at the same time the wires are separated by etching the silicon germanium layer 906. Accordingly, the initial wires formed from silicon layers 904 and 908 begin thicker and are thinned to a size suitable for a channel region in a nanowire device, independent from the sizing of the source and drain regions of the device. Thus, in an embodiment, forming the channel region includes removing a portion of the nanowire, and the resulting perimeters of the source and drain regions (described below) are greater than the perimeter of the resulting channel region.

In accordance with an embodiment of the present disclosure, following removal of the three sacrificial gates 912A, 912B, and 912C and removal of the portions of the silicon germanium layer 906 and the portion of the insulating silicon dioxide layer 902B of the fin structure 910 from the regions originally covered by the three sacrificial gates 912A, 912B, and 912C, a fabrication process is performed that provides a gate-all-around integrated circuit structure having a depopulated channel structure, examples of which are described above in association with FIGS. 2 and 3A-3D. For example, in one embodiment, nanowire 904 is an oxide nanowire in the channel region. In one embodiment, an oxide nanowire includes an oxidation catalyst layer thereon.

The method may also include forming a gate electrode stack surrounding the entire perimeter of the channel region. In the specific example showing the formation of three gate structures over the two silicon nanowires, FIG. 9E illustrates the structure following deposition of a gate dielectric layer 922 (such as a high-k gate dielectric layer) and a gate electrode layer 924 (such as a metal gate electrode layer), and subsequent polishing, in between the spacers 918. That is, gate structures are formed in the trenches 921 of FIG. 9D. Additionally, FIG. 9E depicts the result of the subsequent removal of the interlayer dielectric layer 920 after formation of the permanent gate stack. The portions of the silicon germanium layer 906 and the portion of the insulating silicon dioxide layer 902B of the fin structure 910 are also removed in the regions originally covered by the portion of the interlayer dielectric layer 920 depicted in FIG. 9D. Discrete portions of the silicon layers 904 and 908 thus remain, as depicted in FIG. 9E.

The method may also include forming a pair of source and drain regions in the nanowire, on either side of the channel region, each of the source and drain regions having a perimeter orthogonal to the length of the channel region. Specifically, the discrete portions of the silicon layers 904 and 908 shown in FIG. 9E will, in one embodiment, ultimately become at least a portion of the source and drain regions in a nanowire-based device. In one such embodiment, epitaxial source or drain structures are formed by merging epitaxial material around existing nanowires 904 and 908. In another embodiment, epitaxial source or drain structures are embedded, e.g., portions of nanowires 904 and 908 are removed and then source or drain (S/D) growth is performed. In the latter case, in accordance with an embodiment of the present disclosure, such epitaxial source or drain structures may be non-discrete, as exemplified in association with FIGS. 8A and 8B, or may be discrete, as exemplified in association with FIG. 4J. In either case, in one embodiment, source or drain structures are N-type epitaxial source or drain structures, both including phosphorous dopant impurity atoms.

The method may subsequently include forming a pair of contacts, a first of the pair of contacts completely or nearly completely surrounding the perimeter of the source region, and a second of the pair of contacts completely or nearly completely surrounding the perimeter of the drain region. In an embodiment, the pair of contacts is an asymmetric pair of source and drain contact structures, such as described in association with FIG. 4J. In other embodiments, the pair of contacts is a symmetric pair of source and drain contact structures. Specifically, contacts are formed in the trenches 925 of FIG. 9E following epitaxial growth. One of the trenches may first be recessed further than the other of the trenches. In an embodiment, the contacts are formed from a metallic species. In one such embodiment, the metallic species is formed by conformally depositing a contact metal and then filling any remaining trench volume. The conformal aspect of the deposition may be performed by using chemical vapor deposition (CVD), atomic layer deposition (ALD), or metal reflow.

In an embodiment, as described throughout, an integrated circuit structure includes non-planar devices such as, but not limited to, a finFET or a tri-gate device with corresponding one or more overlying nanowire structures. In such an embodiment, a corresponding semiconducting channel region is composed of or is formed in a three-dimensional body with one or more discrete nanowire channel portions overlying the three-dimensional body. In one such embodiment, the gate structures surround at least a top surface and a pair of sidewalls of the three-dimensional body, and further surrounds each of the one or more discrete nanowire channel portions.

In an embodiment, as described throughout, a substrate may be composed of a semiconductor material that can withstand a manufacturing process and in which charge can migrate. In an embodiment, the substrate is a bulk substrate composed of a crystalline silicon, silicon/germanium or germanium layer doped with a charge carrier, such as but not limited to phosphorus, arsenic, boron or a combination thereof, to form an active region. In one embodiment, the concentration of silicon atoms in a bulk substrate is greater than 97%. In another embodiment, a bulk substrate is composed of an epitaxial layer grown atop a distinct crystalline substrate, e.g. a silicon epitaxial layer grown atop a boron-doped bulk silicon mono-crystalline substrate. A bulk substrate may alternatively be composed of a group III-V material. In an embodiment, a bulk substrate is composed of a III-V material such as, but not limited to, gallium nitride, gallium phosphide, gallium arsenide, indium phosphide, indium antimonide, indium gallium arsenide, aluminum gallium arsenide, indium gallium phosphide, or a combination thereof. In one embodiment, a bulk substrate is composed of a III-V material and the charge-carrier dopant impurity atoms are ones such as, but not limited to, carbon, silicon, germanium, oxygen, sulfur, selenium or tellurium.

In an embodiment, as described throughout, a trench isolation layer may be composed of a material suitable to ultimately electrically isolate, or contribute to the isolation of, portions of a permanent gate structure from an underlying bulk substrate or isolate active regions formed within an underlying bulk substrate, such as isolating fin active regions. For example, in one embodiment, a trench isolation layer is composed of a dielectric material such as, but not limited to, silicon dioxide, silicon oxy-nitride, silicon nitride, or carbon-doped silicon nitride.

In an embodiment, as described throughout, self-aligned gate endcap isolation structures may be composed of a material or materials suitable to ultimately electrically isolate, or contribute to the isolation of, portions of permanent gate structures from one another. Exemplary materials or material combinations include a single material structure such as silicon dioxide, silicon oxy-nitride, silicon nitride, or carbon-doped silicon nitride. Other exemplary materials or material combinations include a multi-layer stack having lower portion silicon dioxide, silicon oxy-nitride, silicon nitride, or carbon-doped silicon nitride and an upper portion higher dielectric constant material such as hafnium oxide.

Embodiments disclosed herein may be used to manufacture a wide variety of different types of integrated circuits and/or microelectronic devices. Examples of such integrated circuits include, but are not limited to, processors, chipset components, graphics processors, digital signal processors, micro-controllers, and the like. In other embodiments, semiconductor memory may be manufactured. Moreover, the integrated circuits or other microelectronic devices may be used in a wide variety of electronic devices known in the arts. For example, in computer systems (e.g., desktop, laptop, server), cellular phones, personal electronics, etc. The integrated circuits may be coupled with a bus and other components in the systems. For example, a processor may be coupled by one or more buses to a memory, a chipset, etc. Each of the processor, the memory, and the chipset, may potentially be manufactured using the approaches disclosed herein.

FIG. 10 illustrates a computing device 1000 in accordance with one implementation of an embodiment of the present disclosure. The computing device 1000 houses a board 1002. The board 1002 may include a number of components, including but not limited to a processor 1004 and at least one communication chip 1006. The processor 1004 is physically and electrically coupled to the board 1002. In some implementations the at least one communication chip 1006 is also physically and electrically coupled to the board 1002. In further implementations, the communication chip 1006 is part of the processor 1004.

Depending on its applications, computing device 1000 may include other components that may or may not be physically and electrically coupled to the board 1002. These other components include, but are not limited to, volatile memory (e.g., DRAM), non-volatile memory (e.g., ROM), flash memory, a graphics processor, a digital signal processor, a crypto processor, a chipset, an antenna, a display, a touchscreen display, a touchscreen controller, a battery, an audio codec, a video codec, a power amplifier, a global positioning system (GPS) device, a compass, an accelerometer, a gyroscope, a speaker, a camera, and a mass storage device (such as hard disk drive, compact disk (CD), digital versatile disk (DVD), and so forth).

The communication chip 1006 enables wireless communications for the transfer of data to and from the computing device 1000. The term “wireless” and its derivatives may be used to describe circuits, devices, systems, methods, techniques, communications channels, etc., that may communicate data through the use of modulated electromagnetic radiation through a non-solid medium. The term does not imply that the associated devices do not contain any wires, although in some embodiments they might not. The communication chip 1006 may implement any of a number of wireless standards or protocols, including but not limited to Wi-Fi (IEEE 802.11 family), WiMAX (IEEE 802.16 family), IEEE 802.20, long term evolution (LTE), Ev-DO, HSPA+, HSDPA+, HSUPA+, EDGE, GSM, GPRS, CDMA, TDMA, DECT, Bluetooth, derivatives thereof, as well as any other wireless protocols that are designated as 3G, 4G, 5G, and beyond. The computing device 1000 may include a plurality of communication chips 1006. For instance, a first communication chip 1006 may be dedicated to shorter range wireless communications such as Wi-Fi and Bluetooth and a second communication chip 1006 may be dedicated to longer range wireless communications such as GPS, EDGE, GPRS, CDMA, WiMAX, LTE, Ev-DO, and others.

The processor 1004 of the computing device 1000 includes an integrated circuit die packaged within the processor 1004. The integrated circuit die of the processor 1004 may include one or more structures, such as gate-all-around integrated circuit structures having depopulated channel structures built in accordance with implementations of embodiments of the present disclosure. The term “processor” may refer to any device or portion of a device that processes electronic data from registers and/or memory to transform that electronic data into other electronic data that may be stored in registers and/or memory.

The communication chip 1006 also includes an integrated circuit die packaged within the communication chip 1006. The integrated circuit die of the communication chip 1006 may include one or more structures, such as gate-all-around integrated circuit structures having depopulated channel structures built in accordance with implementations of embodiments of the present disclosure.

In further implementations, another component housed within the computing device 1000 may contain an integrated circuit die that includes one or structures, such as gate-all-around integrated circuit structures having depopulated channel structures built in accordance with implementations of embodiments of the present disclosure.

In various implementations, the computing device 1000 may be a laptop, a netbook, a notebook, an ultrabook, a smartphone, a tablet, a personal digital assistant (PDA), an ultra mobile PC, a mobile phone, a desktop computer, a server, a printer, a scanner, a monitor, a set-top box, an entertainment control unit, a digital camera, a portable music player, or a digital video recorder. In further implementations, the computing device 1000 may be any other electronic device that processes data.

FIG. 11 illustrates an interposer 1100 that includes one or more embodiments of the present disclosure. The interposer 1100 is an intervening substrate used to bridge a first substrate 1102 to a second substrate 1104. The first substrate 1102 may be, for instance, an integrated circuit die. The second substrate 1104 may be, for instance, a memory module, a computer motherboard, or another integrated circuit die. Generally, the purpose of an interposer 1100 is to spread a connection to a wider pitch or to reroute a connection to a different connection. For example, an interposer 1100 may couple an integrated circuit die to a ball grid array (BGA) 1106 that can subsequently be coupled to the second substrate 1104. In some embodiments, the first and second substrates 1102/1104 are attached to opposing sides of the interposer 1100. In other embodiments, the first and second substrates 1102/1104 are attached to the same side of the interposer 1100. And in further embodiments, three or more substrates are interconnected by way of the interposer 1100.

The interposer 1100 may be formed of an epoxy resin, a fiberglass-reinforced epoxy resin, a ceramic material, or a polymer material such as polyimide. In further implementations, the interposer may be formed of alternate rigid or flexible materials that may include the same materials described above for use in a semiconductor substrate, such as silicon, germanium, and other group III-V and group IV materials.

The interposer may include metal interconnects 1108 and vias 1110, including but not limited to through-silicon vias (TSVs) 1112. The interposer 1100 may further include embedded devices 1114, including both passive and active devices. Such devices include, but are not limited to, capacitors, decoupling capacitors, resistors, inductors, fuses, diodes, transformers, sensors, and electrostatic discharge (ESD) devices. More complex devices such as radio-frequency (RF) devices, power amplifiers, power management devices, antennas, arrays, sensors, and MEMS devices may also be formed on the interposer 1100. In accordance with embodiments of the disclosure, apparatuses or processes disclosed herein may be used in the fabrication of interposer 1100 or in the fabrication of components included in the interposer 1100.

Thus, embodiments of the present disclosure include gate-all-around integrated circuit structures having depopulated channel structures, and methods of fabricating gate-all-around integrated circuit structures having depopulated channel structures.

The above description of illustrated implementations of embodiments of the disclosure, including what is described in the Abstract, is not intended to be exhaustive or to limit the disclosure to the precise forms disclosed. While specific implementations of, and examples for, the disclosure are described herein for illustrative purposes, various equivalent modifications are possible within the scope of the disclosure, as those skilled in the relevant art will recognize.

These modifications may be made to the disclosure in light of the above detailed description. The terms used in the following claims should not be construed to limit the disclosure to the specific implementations disclosed in the specification and the claims. Rather, the scope of the disclosure is to be determined entirely by the following claims, which are to be construed in accordance with established doctrines of claim interpretation.

Example Embodiment 1

An integrated circuit structure includes a vertical arrangement of nanowires. All nanowires of the vertical arrangement of nanowires are oxide nanowires. A gate stack is over the vertical arrangement of nanowires, around each of the oxide nanowires. The gate stack includes a conductive gate electrode.

Example Embodiment 2

The integrated circuit structure of example embodiment 1, further including a gate contact above the vertical arrangement of nanowires. The gate contact is in contact with a top surface of the conductive gate electrode. An interconnect structure is below the vertical arrangement of nanowires. A conductive via of the interconnect structure is in contact with a bottom surface of the conductive gate electrode. The conductive gate electrode acts as a conductive via between the gate contact and the interconnect structures.

Example Embodiment 3

The integrated circuit structure of example embodiment 1 or 2, wherein the oxide nanowires of the vertical arrangement of nanowires have an oxidation catalyst layer thereon.

Example Embodiment 4

An integrated circuit structure includes a first vertical arrangement of nanowires. The first vertical arrangement of nanowires has one or more oxide nanowires. A first gate stack is over the vertical arrangement of nanowires and around the one or more oxide nanowires of the first vertical arrangement of nanowires. A second vertical arrangement of nanowires is above the first vertical arrangement of nanowires. The second vertical arrangement of nanowires has one or more active nanowires. A second gate stack is over the second vertical arrangement of nanowires and around the one or more active nanowires of the second vertical arrangement of nanowires.

Example Embodiment 5

The integrated circuit structure of example embodiment 4, wherein the one or more oxide nanowires of the first vertical arrangement of nanowires have an oxidation catalyst layer thereon.

Example Embodiment 6

The integrated circuit structure of example embodiment 5, wherein the oxidation catalyst layer includes aluminum oxide.

Example Embodiment 7

The integrated circuit structure of example embodiment 4, 5 or 6, further including epitaxial source or drain structures at ends of the first and second vertical arrangement of nanowires.

Example Embodiment 8

The integrated circuit structure of example embodiment 7, wherein the epitaxial source or drain structures are discrete epitaxial source or drain structures.

Example Embodiment 9

The integrated circuit structure of example embodiment 7, wherein the epitaxial source or drain structures are non-discrete epitaxial source or drain structures.

Example Embodiment 10

The integrated circuit structure of example embodiment 7, 8 or 9, wherein the first and second gate stacks have dielectric sidewall spacers, and the epitaxial source or drain structures are embedded epitaxial source or drain structures extending beneath the dielectric sidewall spacers of the first and second gate stacks.

Example Embodiment 11

The integrated circuit structure of example embodiment 7, 8, 9 or 10, further including a pair of conductive contact structures coupled to the epitaxial source or drain structures.

Example Embodiment 12

The integrated circuit structure of example embodiment 11, wherein the pair of conductive contact structures is an asymmetric pair of conductive contact structures.

Example Embodiment 13

The integrated circuit structure of example embodiment 4, 5, 6, 7, 8, 9, 10, 11 or 12, wherein the first vertical arrangement of nanowires is over a fin.

Example Embodiment 14

The integrated circuit structure of example embodiment 4, 5, 6, 7, 8, 9, 10, 11, 12 or 13, wherein the first gate stack includes a first high-k gate dielectric layer and a first metal gate electrode, and the second gate stack includes a second high-k gate dielectric layer and a second metal gate electrode.

Example Embodiment 15

An integrated circuit structure includes a first vertical arrangement of nanowires and a second vertical arrangement of nanowires. The first vertical arrangement of nanowires has an active uppermost nanowire and an oxide bottommost nanowire, the second vertical arrangement of nanowires has an oxide uppermost nanowire and an active bottommost nanowire, and the first and second vertical arrangements of nanowires having co-planar uppermost nanowires and co-planar bottommost nanowires. A first gate structure is over the first vertical arrangement of nanowires. A second gate structure is over the second vertical arrangement of nanowires.

Example Embodiment 16

The integrated circuit structure of example embodiment 15, wherein the nanowires of the first vertical arrangement of nanowires have a horizontal width the same as a horizontal width of the nanowires of the second vertical arrangement of nanowires.

Example Embodiment 17

The integrated circuit structure of example embodiment 15, wherein the nanowires of the first vertical arrangement of nanowires have a horizontal width greater than a horizontal width of the nanowires of the second vertical arrangement of nanowires.

Example Embodiment 18

The integrated circuit structure of example embodiment 15, wherein the nanowires of the first vertical arrangement of nanowires have a horizontal width less than a horizontal width of the nanowires of the second vertical arrangement of nanowires.

Example Embodiment 19

The integrated circuit structure of example embodiment 15, 16, 17 or 18, further including first epitaxial source or drain structures at ends of the first vertical arrangement of nanowires, and second epitaxial source or drain structures at ends of the second vertical arrangement of nanowires.

Example Embodiment 20

The integrated circuit structure of example embodiment 19, wherein the first and second epitaxial source or drain structures are discrete first and second epitaxial source or drain structures.

Example Embodiment 21

The integrated circuit structure of example embodiment 19, wherein the first and second epitaxial source or drain structures are non-discrete first and second epitaxial source or drain structures.

Example Embodiment 22

The integrated circuit structure of example embodiment 19, 20 or 21, wherein the first gate structure has dielectric sidewall spacers, and the first epitaxial source or drain structures are first embedded epitaxial source or drain structures extending beneath the dielectric sidewalls spacers of the first gate structure, and wherein the second gate structure has dielectric sidewall spacers, and the second epitaxial source or drain structures are second embedded epitaxial source or drain structures extending beneath the dielectric sidewalls spacers of the second gate structure.

Example Embodiment 23

The integrated circuit structure of example embodiment 19, 20, 21 or 22, further including a first pair of conductive contact structures coupled to the first epitaxial source or drain structures, and a second pair of conductive contact structures coupled to the second epitaxial source or drain structures.

Example Embodiment 24

The integrated circuit structure of example embodiment 15, 16, 17, 18, 19, 20, 21, 22 or 23, wherein the first vertical arrangement of nanowires is over a first fin, and the second vertical arrangement of nanowires is over a second fin.

Example Embodiment 25

The integrated circuit structure of example embodiment 15, 16, 17, 18, 19, 20, 21, 22, 23 or 24, further including a gate endcap isolation structure between and in contact with the first gate structure and the second gate structure. 

What is claimed is:
 1. An integrated circuit structure, comprising: a first vertical arrangement of nanowires, the first vertical arrangement of nanowires having one or more oxide nanowires, wherein a bottommost one of the first vertical arrangement of nanowires is a first one of the one or more oxide nanowires, and an uppermost one of the first vertical arrangement of nanowires is an active nanowire; a first gate stack over the first vertical arrangement of nanowires and around the one or more oxide nanowires of the first vertical arrangement of nanowires and around the active nanowire of the first vertical arrangement of nanowires; a second vertical arrangement of nanowires above the first vertical arrangement, the second vertical arrangement of nanowires consisting of one or more active nanowires; and a second gate stack over the second vertical arrangement of nanowires and around the one or more active nanowires of the second vertical arrangement of nanowires.
 2. The integrated circuit structure of claim 1, wherein the one or more oxide nanowires of the first vertical arrangement of nanowires have an oxidation catalyst layer thereon.
 3. The integrated circuit structure of claim 2, wherein the oxidation catalyst layer comprises aluminum oxide.
 4. The integrated circuit structure of claim 1, further comprising: epitaxial source or drain structures at ends of the first and second vertical arrangements of nanowires.
 5. The integrated circuit structure of claim 4, wherein the epitaxial source or drain structures are discrete epitaxial source or drain structures.
 6. The integrated circuit structure of claim 4, wherein the epitaxial source or drain structures are non-discrete epitaxial source or drain structures.
 7. The integrated circuit structure of claim 4, wherein the first and second gate stacks have dielectric sidewall spacers, and the epitaxial source or drain structures are embedded epitaxial source or drain structures extending beneath the dielectric sidewall spacers of the first and second gate stacks.
 8. The integrated circuit structure of claim 4, further comprising: a pair of conductive contact structures coupled to the epitaxial source or drain structures.
 9. The integrated circuit structure of claim 8, wherein the pair of conductive contact structures is an asymmetric pair of conductive contact structures.
 10. The integrated circuit structure of claim 1, wherein the first vertical arrangement of nanowires is over a fin.
 11. The integrated circuit structure of claim 1, wherein the first gate stack comprises a first high-k gate dielectric layer and a first metal gate electrode, and the second gate stack comprises a second high-k gate dielectric layer and a second metal gate electrode. 